Abstracts

Rationale: Organophosphate (OP) compounds include nerve gas and pesticides. OPs act by irreversibly inhibiting the enzyme acetylcholinesterase, causing a cholinergic crisis that evolves into status epilepticus (SE). While advances have been made to treat the seizures and cholinergic crisis from OP exposure, at present there are no effective therapies to significantly reduce the mortality associated with survival from OP SE. To address this need, we investigated whether treatment with a novel intramuscular (i.m.) adjunct therapy of atenolol (AT) and levetiracetam (LV) would protect the heart and the brain from SE vulnerability and extend significant protection from mortality when administered after the OP exposure. Methods: Male Sprague-Dawley rats (250-300g) were injected with POX (2 mg/kg, s.c). One minute later, rats were injected with atropine sulfate (0.5 mg/kg, i.m.) and 2-PAM (25 mg/kg, i.m). Rats quickly developed SE, which was then stopped with midazolam (2 mg/kg, i.m.) at 1-h post SE onset. Rats were than treated with AT (5 mg/kg, i.m.) and LV (50 mg/kg, i.m.) b.i.d. alone or in combination. To evaluate optimal treatment durations, drugs were administered for 2, 7, or 14-days alone and in combination. Mortality was assessed at 30-days after the end of the adjunct therapies. Results: POX exposure produced rapid onset of SE that was treated effectively with atropine, 2-PAM and midazolam therapy. Percent mortality assessed 30-d post POX SE was 33 ± 6%. When administered for 2-days, AT-only therapy reduced mortality by 12 ± 3%. LV-only therapy reduced mortality by 16 ± 5%. AT+LV produced a 40 ± 7% reduction in mortality. When administered for 7-days, AT-only therapy produced a 10 ± 4% reduction in mortality. LV-only therapy produced a 20 ± 5% reduction in mortality. AT+LV reduced mortality by 67 ± 2%. When administered for 14-days, AT-only and LV-only therapy produced 9 ± 2% and 15 ± 6% reductions in SE mortality respectively. AT+LV reduced mortality by a 66 ±6%. Further analysis revealed that 7-d AT+LV therapy was significantly better than 2-d AT+LV therapy but the 14-day AT+LV therapy was not better than the 7-d treatment in reducing mortality. Conclusions: Our data provide the first evidence that mortality from POX SE can be significantly reduced by i.m. treatment with AT and LV. We established that the 7 day treatment protocol with AT and LV was optimal to reduce mortality. We also demonstrated that the combination of AT and LV was superior to either agent alone in reducing mortality. In addition, our studies have provided the first direct evidence that the i.m. route of administration of AT and LV is an effective method to deliver AT and LV. AT is a beta-adrenergic blocker and acts to reduce cardiac stress following SE-induced catecholamine surge while LV is a neuronal calcium-induced calcium release inhibitor and synaptic SV2a inhibitor that exerts a neuroprotective actions. Targeting critical vulnerabilities in heart and brain with AT+LV combination therapy produces significant reductions in mortality following POX SE. Funding: This work was supported by the CounterACT Program, National Institutes of Health Office of the Director (NIH OD), and the National Institute of Neurological Disorders and Stroke Grant No. 1U01NS105058-01 to R.J.D.